1. Field of the Invention
The present invention relates to a process for preparing a laminated plate. More particularly, it relates to a process for preparing a laminated plate by laminating metallic sheets on both surfaces of a thermoplastic synthetic resin.
2. Description of the Prior Art
A laminated plate prepared by laminating metallic sheets on both surfaces of a thermoplastic synthetic resin sheet has been well-known in, for example U.S. Pat. No. 3,382,136 and has been used in various usages as a laminated product having both characteristics of a metal and a thermoplastic synthetic resin (hereinafter referring to as a synthetic resin). Such laminated plate has been continuously prepared by processes including the following steps disclosed in U.S. Pat. No. 3,616,019. That is, the process includes (a) a heating step of heating two sheets of metallic sheets stretched under a constant tension; (b) a laminating step of forming a laminating plate by feeding preheated metallic sheets and a molten synthetic resin sheet between heat-press rolls to place the synthetic resin sheet between the metallic sheets; and (c) a cooling step of cooling the resulting laminated plate.
Thus, one disadvantage of the process is to form creases and waves on the metallic sheet surface of the laminated plate. Such disadvantage of the metallic sheet surface causes inferior appearance in the case of the use of the laminated plate, for example, as a board of a furniture. When the metallic sheet is thinner or the synthetic resin sheet is thicker, the formation of creases or waves is more significant.
Thus, the formation of creases on the metallic sheet surface has been overcome by certain methods. Transverse wave formed on the metallic sheet surface in the direction perpendicular to the stretching direction of the laminated plate has been also overcome. However, any effective process for overcoming longitudinal wave formed on the metallic sheet in the stretching direction of the laminated plate has not been found.
An object of the present invention is to provide a laminated plate having no longitudinal wave on the metallic sheet surface. The object has been easily attained by the process of the present invention.